1. Field of the Disclosure
The present disclosure relates to an apparatus and a method for detecting phase deficiency in an inverter, and a method thereof.
2. Description of Related Art
Generally, an inverter is a device which converts 3-phase direct current (DC) into alternating current (AC).
FIG. 1 is a block diagram illustrating a general inverter, which drives a motor (2).
The inverter (1) converts 3-phase AC power source into DC using a rectifying unit (10), then stores the converted DC in a DC link capacitor (20), and then converts it into AC again using a inverter unit (30) to provide the motor (2) with the converted AC. Additionally, the inverter (1) controls speed of the motor (2) by changing voltages and frequencies.
Here, at least one phase of the inverter output I may be opened. This phenomenon is referred to as “phase deficiency”, which is caused by misconnection between the inverter (1) output end and the motor (2), or by malfunction of a switching device between the inverter (1) output end and the motor (2). When the phase deficiency occurs, an overcurrent exceeding rated current may be applied to the motor (2), causing a burning damage by degradation.
Such a phase deficiency of an inverter may be determined by detecting an output current of the inverter.
FIGS. 2a and 2b are block diagrams illustrating an inverter output current detection unit. FIG. 2a is illustrating a case in which a current transformer (CT) is used, and FIG. 2b is illustrating a case in which a leg-shunt resistor is used, respectively.
As illustrated in FIG. 2a, the CT (41) is arranged on the output line of the inverter (1), and detects 3-phase output current of the inverter unit (30). Meanwhile, as illustrated in FIG. 2b, the leg-shunt resistor (42) is arranged on the emitter end of the insulated gate bipolar transistor (IGBT) on each phase of the inverter unit (30), and detects output current of the inverter unit (30) when the current is flowing to the lower IGBT by switching operation status of the inverter unit (30).
FIG. 3 is an exemplary view illustrating output current detection restricted by switching operation status of an inverter.
As illustrated in FIG. 3, because the current detection area is restricted by switching operation status and current conduction time of the inverter unit (30), in order to expand the current detection area, the inverter output current detection using a leg-shunt resistor takes a process which detects the active 2-phase current among the 3-phase current of the inverter, and then calculates the rest of one phase current. The following is a table showing calculations of current detection in the current detection using a leg-shunt resistor.
TABLE 1SectorInformationIuIvIw1Iu = (Ivs + Iws)Ivs = −IvsIw = −Iws2Iu = −IusIvs = (Ius + Iws)Iw = −Iws3Iu = −IusIvs = (Ius + Iws)Iw = −Iws4Iu = −IusIvs = −IvsIw = (Ius + Ivs)5Iu = −IusIvs = −IvsIw = (Ius + Ivs)6Iu = (Ivs + Iws)Ivs = −IvsIw = −Iws
Such a current detection using a leg-shunt resistor is commonly used for a small inverter of low-price type, because it is able to be performed at lower cost compared to the current detection using a CT.
However, because this current detection method using a leg-shunt resistor is to calculate the rest of one phase current after detecting the active 2-phase current among the 3-phase current of the inverter, there is a problem that a precise detection of the phase deficiency is not available.